PHILADELPHIA (AP) — A bomb threat investigation that prompted a search of a trans-Atlantic flight and questioning of its passengers has turned up nothing suspicious, officials said.

US Airways Flight 777 from Shannon, Ireland, landed in an isolated part of Philadelphia International Airport on Wednesday afternoon and was met on the tarmac by fire trucks and federal and local authorities.

A telephone threat about a bomb was made about the plane before it landed, Philadelphia police Chief Inspector Joe Sullivan said.

The plane’s 171 passengers and eight crew members exited via staircases and were taken to waiting buses. The Boeing 757 was searched by a bomb-sniffing dog, passengers were questioned and their luggage was screened, investigators said.

US Airways said in a statement it was aware of a possible security issue with the flight and “out of an abundance of caution taxied the aircraft to a remote location, where it was met by law enforcement and emergency personnel.”

Nothing was found, and the all-clear was given about an hour later.

Officials did not disclose the specific nature of the bomb threat or details about from where it may have originated. The FBI, Philadelphia police department and Transportation Security Administration were involved in the investigation and said the person who placed the call could face serious criminal charges.

U.S. customs officials have screening facilities at Shannon Airport, and the passengers aboard the plane would have gone through them before boarding.

The plane continued as planned to Pittsburgh after its scheduled stop in Philadelphia. Inbound flights were briefly delayed while the investigation was underway.